Seafloor Mapping

3D bathymetry with contour lines.
Click image to to enlarge.

Ocean Ecology has designed a towfish system to carry out seafloor mapping. A single-beam sounder transducer is mounted in a highly streamlined towfish, and towed at 1.5 m depth from an A-frame at the stern of the Moody Blue. This technique reduces the effects of pitch and roll on the transducer output, which can create significant artifacts in hull-mounted systems.

Ocean Ecology's single beam sounder towfish.

Deployment of the towfish.

The signal from the transducer is processed by a JFC-130 echo sounder, which extracts both depth and bottom hardness components from the signal (to learn more about how bottom hardness and roughness components are extracted from the returned echoes, click here). The output from the JFC-130 echo sounder is combined with the output from a JRC DGPS unit using a multiplexer, and this combined signal is sent to a laptop for further processing, data logging, and realtime display.

Raw NMEA sentences generated by the echo sounder and DGPS unit are logged to the laptop. Realtime translation of the NMEA sentences into latitude, longitude, depth, and hardness values is done by ArcPad, and this data is logged as shape files which can then be imported directly into ArcMap or other GIS programs for further data analysis.

After all bathymetic data has been collected for a site, the data is corrected for towfish depth (usually 1.5 m) and tidal height in ArcMap. This corrected data is exported from ArcMap, and used to generate contours in Surfer. These contour maps can be imported back into a GIS program for further analyses.

Shown below is typical example of the type of data which can be generated by our seafloor mapping system as viewed in ArcScene.

3D bathymetry.
Click image to enlarge.

This image shows a three-dimensional depth plot with purple colors representing deeper depths and green colors representing shallower depths.

Click on this image to view an interactive 3-dimensional model
of the bathymetry shown above.

3D bottom hardness.
Click image to enlarge.

This image above shows bottom hardness overlain on the three-dimensional depth plot. Reds and browns represent rock bottom, whereas blues and purples represent softer sediments. Note the presence of softer sediments around the edges of the depression (which was located at the center of the bay). These softer sediments represent areas of sand which accumulated in the shallower regions of the bay to form beaches.

Click on this image to view an interactive 3-dimensional model
of the bottom hardness shown above.